In the field of positive displacement fluid apparatus, there exists a class or category generally referred to as scroll-type fluid apparatus which are characterized by the provision of wrap elements defining flank surfaces of generally spiroidal configuration about respective axes, which wrap elements lie in intermeshing, angularly offset relationship with their axes generally parallel such that relative orbital motion between the wrap elements results in the formation of one or more moving volumes between the wrap elements, defined by moving lines of coaction between the wrap elements at which their flank surfaces lie substantially tangent to each other. In a preferred form, the precise shape of the generally spiroidal flank surfaces comprise an involute of a circle, however, the term "generally spiroidal" is intended to encompass any form providing the requisite moving volumes during relative orbital motion between the wrap elements. Typically, end plate means are provided in sealing relationship to the wrap elements as they undergo relative orbital motion such that the moving volumes are effectively sealed. Reference may be had to U.S. Pat. No. 801,182 for an early disclosure of scroll-type fluid apparatus embodying this principle, or to U.S. Pat. No. 3,884,599 for a more recent disclosure.
It has been recognized that scroll-type fluid apparatus have utility in a wide variety of applications, including gas compressors or vacuum pumps for elevating the pressure of a gaseous working fluid; liquid pumps for transporting a liquid working fluid; or as an expansion engine for producing mechanical work by the expansion of a relatively high pressure gaseous working fluid. In the case of a gas compressor, the moving volumes defined between wrap elements originate at a radially outer portion thereof and progress inwardly while their volume is reduced, resulting in compression of the working gas which is then discharged at a radially inner portion of the wrap elements. Liquid pumps function in a similar fashion with the wrap elements configured such that no appreciable reduction in volume occurs at the volumes progress radially inwardly, while scroll-type expansion engines receive a relatively high pressure gaseous working fluid at the radially inner portion of their wrap elements, which then progresses radially outwardly in the moving volumes as they increase in volume, resulting in expansion of the working fluid and production of mechanical work.
In considering the kinematic relationship necessary in order to effect the requisite relative orbital motion between the wrap elements, it should be noted that at least three general approaches exist:
(1) maintaining one wrap element fixed while orbiting the other with respect thereto, i.e., causing it to undergo circular translation while maintaining a fixed angular relationship between the wrap elements; PA1 (2) orbiting both wrap elements in opposite directions while maintaining a fixed angular relationship therebetween; and PA1 (3) rotating both wrap elements about offset, parallel axes while maintaining a fixed angular relationship therebetween.
A second consideration relevant to the relative orbital motion between wrap elements is the manner in which their flank surfaces are permitted to coact with each other; i.e., is actual contact permitted therebetween along the lines at which the surfaces lie substantially tangent, accompanied by a radial sealing force therebetween; or are constraints imposed thereon so as to maintain a slight clearance or gap therebetween. In this regard, it is convenient to term the former as "radially compliant" type, while the latter may be referred to as "fixed-crank" type. As used herein, the term "moving line coaction" is intended to be descriptive of both types, while the term "actual moving line contact" is limited to the radially compliant type. Reference may be had to U.S. Pat. No. 3,924,977 for disclosure of a radially compliant type drive mechanism, while U.S. Pat. No. 4,082,484 is illustrative of the fixed-crank type.
Reference may be had to the aforementioned U.S. Pat. No. 801,182 for an early disclosure of a tip seal for use in scroll apparatus, while U.S. Pat. No. 3,994,636 is illustrative of a more recent development in this area. In both these references, however, it is apparent that the seal element itself is constructed from a single strip of material, the '636 patent suggesting both metallic or nonmetallic materials including cast iron, steel, bronze, carbon, or plastics such as polytetrafluoroethylene, or polyamides. As will be appreciated, the use of a single strip of material in order to form the seal element has the drawback that it must be machined or otherwise formed to the precise involute shape of the groove in the wrap element in order to afford proper operation. This requirement is a distinct drawback in the case of preferred metallic sealing elements which require expensive machining operations in order to provide a proper seal, as well as with many plastics materials which are not sufficiently elastic to be formed into the desired shape, which would also require machining or some sort of molding operation in order to be formed.
Reference may also be had to U.S. Pat. No. 4,199,308 for a further disclosure of a tip seal for scroll-type fluid apparatus, wherein the novelty lies in the particular configuration of the groove formed in the wrap element and its cooperating seal element.